Antennas of this type, given a movement of rotation in azimuth, permit the determination of the altitude of the located objects and also the tracking of these objects. However, if it is desired to maintain a surveillance or search during tracking, it is necessary to provide a separate antenna associated with another detecting system.
In commonly owned U.S. Pat. No. 3,448,450 there has been proposed a system wherein a number of radiators or elementary sources are spaced apart vertically and excited simultaneously through respective phase shifters which produce a number of beams stacked in elevation, the angle of elevation of these beams being made variable by concurrent adjustments of the phase shifters. This system is particularly adapted for the evaluation of the altitude of tracked targets and is associated with an additional radar provided with a special antenna rotating in azimuth and effecting a surveillance.
An antenna of such system comprises a number of radiating sources spaced apart vertically and coupled through phase shifters with two feed waveguides parallel to each other. One of these waveguides is connected through a rotary coupling and a multiplexer to three transmitters operating at three different frequencies, the other of these waveguides being connected directly to the receiver of the assembly the couplers connecting that waveguide to the radiating sources impart to the incoming fields a distribution of the difference type. The assembly consequently constitutes a transmitter-receiver operating as a monopulse radar.
In order to effect a surveillance in this instance during the evaluation of the altitude of the objects or their tracking, another radar must be provided.
Thus, such an arrangement requires two different systems with distinct modes of operation, the surveillance system being a panoramic radar in which the rotation of the antenna has to be synchronized with that of the waveguides of the electronically scanned antenna.